Discover the research projects happening at TRACE!

The Sabana Field Research Station, located in El Yunque National Forest in eastern Puerto Rico, is the home of the warming experiment Tropical Responses to Altered Climate Experiment, better known as TRACE. This long-term experiment, which involves heating three plots (of approximately 12 sq. m each) to ~4°C above the ambient temperature using infrared heaters, aims to understand how global change and hurricanes impact tropical forests, particularly focusing on carbon and nutrient cycling. However, within such a large-scale undertaking, there is a wide range of different research questions constantly being pursued by scientists with diverse interests and backgrounds.

During the summer months, I worked as a TRACE intern and had the opportunity to assist and learn about many of these different endeavors. In this blog, I am going to dive into four of the many fascinating research projects being conducted at TRACE and what it was like to work on them. While this research is incredibly important and cutting-edge, I also want to demystify what it actually looks like to conduct this research, because as someone entering science myself, I have often felt intimidated and overwhelmed. Along the way, I will also introduce you to some of the scientists, from undergraduate interns (like myself) to PhD students and technicians, who are pursuing these questions.

Projects 

Herbaceous census

This summer, one of my favorite experiences was conducting an herbaceous census, a process that is undertaken annually by TRACE technicians and interns. The goal of this census is to understand how rising temperatures, simulated by the experimental warming in the TRACE plots, might impact the composition and abundance of herbaceous understory plants in tropical rainforests. The census started with a training from technician and resident plant expert, Laura Rubio Lebrón, on the different herbaceous plant species that we would likely find in the six experimental sites (3 control plots; 3 warmed plots). Then, armed with PVC square quadrats used to divide the plots into smaller subplots, a camera, and a guide to plant species, we got started.

For each of the individual subplots, we had to estimate the percent area of herbaceous plant cover, the percent area of woody plant cover, the percent area of each of the herbaceous plant groups, and the number of individuals of each herbaceous plant species. You wouldn’t guess that this process would require negotiation skills, but in addition to taking photos to be used by a computer program, we also had to come to a consensus on estimates in the field. This led to countless conversations going something along the lines of: “I think vines cover 30%” and someone else chiming in, “I would say 25% actually”. Finally, someone would say, “well, how do we all feel about 28% vines?” to which everyone would respond with at least semi-enthusiastic assent before we moved on to the next estimate. This census took many hours of debating percentages, trying to get the PVC squares to fit under roots or around plants, and constantly playing Twister to avoid stepping on little seedlings in the plot. However, we did eventually finish collecting this important data from all 6 TRACE plots (with 12 subplots in each), and now none of us can go anywhere without seeing and identifying herbaceous plant species everywhere we look.

Minirhizotron root imaging

If anyone asks what technician Laura Rubio Lebrón is doing at any given moment, it would be a safe bet to assume that she is busy analyzing infinite images of roots. I’m barely exaggerating since the last I heard, she had more than 80,000 photos left, and the numbers are only growing as she continues to sample! Roots play important roles in tropical ecosystems, from facilitating plant nutrient and water acquisition to contributing to soil respiration and organic carbon, making them a measure of ecosystem health and change. The Minirhizotron, basically a 1 m long clear tube installed in the ground into which a specialized camera can be inserted, is a system used to monitor belowground root systems.

Every two weeks, Laura goes out with a stool and a fancy camera to take photos from the two Minirhizotron tubes in each of the 6 TRACE plots. The Minirhizotron camera, attached to a long extension, is inserted into the tube and can even connect to her phone to see the roots in real-time, make sure there’s a clear image, and take pictures. There is a mechanism that moves the camera up the tube at regular intervals, allowing her to capture the same exact photos every time she samples and monitor how the roots in that frame are changing over time. The goal is to understand how global change may affect tropical rainforest root systems by looking at how root diameter, depth, and mortality change in the warmed plots compared to the controls over time. However, every image taken has to be individually analyzed to measure the root diameter and determine whether any new roots have appeared or died. Analyzing the images taken post-hurricanes Irma and María is still ongoing, but will provide valuable insight into what we might expect to happen in tropical forest root systems as temperatures rise due to global change.

To see minirhizotron results by Dr. Daniella Yaffar see here.

Daliz’s stomata experiment

Over the course of the summer, all of the undergraduate interns (including myself) got to work with the technicians and Dr. Tana Wood, US Forest Service Research Ecologist and TRACE PI, to develop their own independent project on a topic of interest. Although we all helped each other, I worked particularly closely with Daliz Casablanca Sánchez, an undergraduate student attending the University of Puerto Rico at Cayey. Her project is focused on investigating the effects of the warming experiment on stomata, which are tiny pores found primarily on plant leaves (but also sometimes other parts), crucial for gas exchange in photosynthesis and regulating water movement. Daliz is looking at how the warming experiment at TRACE is impacting the size and density of stomata in three different plant species in both the seedling and adult stages. For this project, we used a surprisingly simple but effective method of painting leaves with a thin coat of clear nail polish and then removing this dried layer with a piece of tape and sticking it to a microscope slide. While drying on the leaves, the nail polish basically creates a mold of the shape of the stomata, allowing each one to be measured and counted easily when viewed under a microscope. And if my biology career path doesn’t work out, perhaps the many hours of painting the leaves of little seedlings will have prepared me for a job as a nail technician!

Some previous stomata results can be seen here!

Rachel’s PhD research

One of the things I enjoyed most about working with TRACE as an undergraduate intern was getting to meet and learn from scientists at all stages in their careers. In particular, as someone considering my options after graduation, it was particularly valuable to work with and talk to PhD candidate Rachel Cruz-Pérez, who comes to TRACE during the summers to collect data for her dissertation. Rachel is studying soil biogeochemistry at Penn State University, and her research focuses on carbon cycling. As I learned from her, both microbes and roots in the soil respire (meaning produce CO₂), and together, these processes make up soil respiration, which is the largest terrestrial source of carbon in the atmosphere. Through her research at TRACE, Rachel is trying to disentangle the relative contribution of microbes and roots to overall soil respiration at different depths and understand how this is impacted by the experimental warming.

As an intern, I was able to help her in the field as she used the LI-COR smart chamber (a portable device for assessing soil gas fluxes) to measure CO₂ production over time and take gas samples, which she will analyze later in her lab. I also spent many hours in the lab picking roots out of the soil samples she collects. This allows her to do laboratory experiments, separating root respiration from microbial respiration. As if her research wasn’t impressive enough, for the last chapter of her dissertation, she also plans to create a documentary on soil dynamics geared towards non-scientists. This is an incredible example of science communication, which describes the various ways that scientists share their knowledge and involve their communities, which is ultimately what helps to create awareness and enthusiasm for important research.

Final Thoughts

Every one of these projects, along with the many others occurring at TRACE, is shedding light on how global change will affect tropical forests in the future. When I started as an intern, this research all felt daunting and incomprehensible, and yet, as I finished my two months working at TRACE, I discovered that I could explain more than I ever would’ve thought possible. I participated in many different aspects of the research process, from collecting data for various projects to troubleshooting broken sensors and even working on my own independent project. However, what I have taken away from this experience is far more than the many surprising skills (like painting leaves or discussing the exact percent area covered in leaves) or vast amounts of scientific knowledge. Instead, I learned the value of approaching new things with curiosity rather than fear of not knowing something. For the most part, I had very minimal knowledge of the science before tackling any of the tasks given to me, but I learned an incredible amount from simply asking questions and listening to the many brilliant people who know so much and were always willing to explain things (even multiple times when I didn’t get it the first time). I think that students and early career scientists, like myself, often are afraid of admitting that we don’t know something, but my experiences this summer taught me that being unsure, confused, and baffled is actually what being a scientist is all about. As we keep questioning and learning from those around us, we eventually reach the questions to which there aren’t answers yet–or at least not until we create an experiment to find out!